It is important to maintain the confidentiality of a user equipment's (UE's) long-term subscription identifier (e.g., an IMSI (International Mobile Subscriber Identity)). Early generation 3GPP systems (e.g., 4G/LTE, 3G/UMTS, 2G/GSM) included a partial mechanism for long-term subscription identifier confidentiality using one or more short-term subscription identifiers. GUTI (Globally Unique Temporary ID) and C-RNTI (Cell-Radio Network Temporary Identifier) are examples of short-term subscription identifiers in 4G/LTE systems. However, the legacy partial mechanism may expose the long-term subscription identifier in clear text over the air interface. For example, so-called “IMSI catchers” could simply ask the long-term identifier from the UE, e.g., using identifier request/response messages.
The 3rd Generation Partnership Project (3GPP) currently discusses how security, such as privacy, can be improved in communications networks. With respect to 5G, the 3GPP TS 33.501 V0.2.0 mentions a Subscription Permanent Identifier (SUPI) and it is there noted that the SUPI may be concealed, e.g. in the form of a pseudonym or a public-key encrypted SUPI.